There are two prior art commonly used ways to measure the properties of a surface under test. The first method requires visual inspection in which a technician closely examines the surface under test (SUT) for damage and defects, and compares suspected damage to previously recorded inspections. The visual inspection is performed using visible light or can be performed with IR or microwave imagers. The second method uses handheld probes that the technician meticulously scans across the SUT. The handheld probe typically evaluates a small area at a time.
Both of these methods are very time consuming, and difficult to perform on SUTs that lie on concave surfaces with small openings. Visual inspection methods are subjective and open to interpretation.
Also in the prior art are health monitoring systems that use acoustic surface waves (ASW) to determine structural mechanical properties. While the ASW methods can be used to monitor mechanical health, the ASW methods are not suited for detecting changes in static/lightning charge dissipation and RF properties in the SUT, especially at electromagnetic frequencies greater than 1.0 GHz. ASW methods monitor only the mechanical properties of the SUT.
In U.S. Pat. No. 7,719,694, issued May 18, 2010, another method is disclosed of using surface wave imaging to detect damage on a surface. A surface wave network (SWN) is described that is integrated within the SUT to allow for rapid real-time in-situ diagnostics. The surface-wave medium described in U.S. Pat. No. 7,719,694 is integral with the SUT and is not removable.
Another method used for evaluating the health of RF surfaces is inverse synthetic aperture radar (ISAR) imaging. ISAR imaging requires the use of expensive equipment and time-consuming processing. It also requires the imaging sensors to be sufficiently removed from the SUT, and ISAR imaging is not capable of measuring SUT properties in concave, re-entrant spaces.
What is needed is a low cost and rapid method of monitoring the material health of a surface under test (SUT) that can be used to monitor the mechanical and RF properties of the SUT, and which is not integral to the SUT. The embodiments of the present disclosure answer these and other needs.